This study is to provide an indepth assessment of a community-based sample of persons who have been previously classified as either having senile dementia or to be high risk for having this disorder. The study includes a clinical examination plus a surveillance by contacting the subject and a close relative or friend every nine months. Comparison will be made with unaffected persons to define risk factors and etiologic events. This is a five year study of a free living population having been identified as positive for senile dementia by a standard screening instrument. The cases and controls will have a clinical examination with valid and quantified measurement techniques and interviews every nine months to obtain demographic, social-psychological, cognitive, medical, drug usage information and health service utilization, and other related information. Similar information will be gathered from a relative or close friend.